The invention relates to a setting device for an adjustable gearing mechanism, in particular for selecting a parking position in an automatic transmission.
Conventional automatic transmissions for automobiles usually have four preselection ranges for the different operating states of the automobile, namely a park position, a reverse position, a neutral position, and a drive position. In the park position, a mechanical locking mechanism (park lock) prevents the output shaft of the automatic transmission, and therefore the wheels of the automobile, from turning, thus preventing the automobile from rolling away unintentionally.
The desired preselection range is set by the driver by actuating a gearshift lever, while the link between the gearshift lever and the automatic transmission can be effected, for example, by means of electric cables, this shifting principle being known as xe2x80x9cshift by wirexe2x80x9d. At the same time it must, however, be ensured that the park lock can also be activated even in the event of a total failure of the vehicle electronics system.
As a solution to this problem, a setting device for an automatic transmission is known from DE 44 22 257 C1, said device comprising, in addition to an electric motor for setting the desired preselection range in normal operation, also a spring which enables the park lock to be activated if the electric motor or the power supply fails. For this purpose, the driver simply has to release the spring, which is under tension during normal operation, by means of a Bowden cable, whereupon the spring activates the park lock.
However, a disadvantage with this known setting device is the fact that in order to activate the park lock in the event of a failure of the power supply, a manual intervention is still required by the driver, in that the latter actuates the Bowden cable.
Furthermore, EP 0 198 114 B1 discloses a setting device for a two-stage gearing mechanism, in which an electric motor axially displaces a rod in order to set the desired gearing mechanism stage, said rod being linked via a spring to a likewise axially movable carriage which carries the selection lever of the gearing mechanism. In this arrangement, the carriage can be locked in two positions by means of a stationary electromagnetically controllable locking element in the form of a solenoid, the two positions of the carriage each corresponding to a gearing mechanism stage. Thus, owing to the locking of the carriage by the locking element, the displacement of the rod by the electric motor does not lead to a change in the gearing mechanism stage, but simply leads to a tensioning of the spring. When the carriage is unlocked, the tensioned spring then drives the carriage into the respective other position, thus causing the other gearing mechanism stage to be set. However, the locking element fixes the carriage in the idle state to ensure that a failure of the power supply or a malfunction of the locking element does not lead to a change in the gearing mechanism stage. Rather, with the known setting device described in the foregoing, in the event of a failure of the power supply the gearing mechanism remains in the gearing mechanism stage just set.
The object of the invention is therefore to create a setting device for an automatic transmission in which the automatic transmission is controlled via electric cables, the park lock being activated automatically even in the event of a total failure of the vehicle electronics system.
The object is achieved, based on a known setting device for an adjustable gearing mechanism according to a setting element having a setting motion; an intermediate gearing mechanism for transferring the setting motion of the setting element to a control element of the adjustable gearing mechanism, the intermediate gearing mechanism comprising a movably mounted carrier linked to the setting element via a spindle, a carriage mounted in a linearly movable manner in parallel with the carrier and linked to the control element, and a controllable locking element to link the carriage to the carrier or separate it from the carrier; and a mechanical energy store for driving the carriage in the event of a failure of the setting element.
The invention comprises the general technical principle of providing a mechanical energy store in addition to the normal mechanical setting element for selecting the preselection range of the automatic transmission, said mechanical energy store enabling the park lock to be activated in the event of a failure of the normal setting element. An energy store of this type preferably comprises a spring, for example in the form of a helical or flat spiral spring, although other types of energy store which permit the park lock to be activated are also possible.
In a conventional automatic transmission, the preselection range of the automatic transmission is usually set via a control shaft, the angle position of which determines the preselection range. However, the rotation of the control shaft usually requires relatively large torques of up to 12 Nm, with the result that the energy needed for selecting the preselection range of the automatic transmission is transmitted by the mechanical setting element to the control shaft determining the preselection range via an intermediate gearing mechanism.
According to the invention, energy is introduced into the intermediate gearing mechanism via a movably mounted carriage, the carriage being linked on one hand to the energy store and on the other hand, via a controllable locking element, to the setting element. In the locked state, the setting element therefore acts on the carriage and thus enables the desired preselection range to be set. If the setting element fails, on the other hand, the locking element is unlocked, with the result that the movably mounted carriage is now linked only to the energy store and is pushed by the latter into the desired position, causing the automatic transmission to assume the desired preselection range. The controllable locking element for linking the carriage to the setting element preferably comprises an electromagnet, such that the locking element is automatically unlocked in the event of a power failure and thus releases the movably mounted carriage.
The carriage is preferably movable in a linear direction, but in principle it is also conceivable that the carriage is moved on a circular path or a path curved in some other way.
In the preferred embodiment, the setting element is linked to a carrier which is movably mounted parallel to the carriage, the locking element either linking the carriage to the carrier or separating it from the carrier. In normal operation with a properly functioning power supply, the locking element therefore links the carriage to the carrier, which is driven by the setting element such that the setting element moves the carriage and thereby sets the desired preselection range of the automatic transmission. If the power supply fails, on the other hand, the locking element severs the link between the carrier and the carriage, with the result that the setting element no longer acts on the carriage, which is then moved into the desired position by the energy store.
In an embodiment of the energy store as a spring, the spring can be disposed, for example, between the carrier and the carriage and can pretension the carrier with respect to the carriage. As an alternative to this, however, it is also possible that the spring is disposed between the carriage and a thrust bearing fixed in space and pretensions the carriage independently of the carrier with respect to the thrust bearing. In both cases, when carriage and carrier are unlocked, the energy of the tensioned spring leads to the carriage being moved by the spring, whereupon the automatic transmission assumes the desired preselection range.
In a variant of the invention, the carrier has a guide for the movable mounting of the carriage, such that the carriage can be moved relative to the carrier. In another variant of the invention, in contrast, a separate guide is provided both for the carrier and for the carriage.